Not applicable.
Not applicable.
The present invention relates to a plant for use in recovering metal from metal ore using a hydrometallurgical process. More specifically, this plant is a modular solvent extraction plant for extracting a metal such as nickel, cobalt, uranium, or copper from its corresponding metal ore. Still further, this plant may include an organic scrub station, which can be used to remove contaminants or other metals from organic solutions used in extracting the metal.
Metal may be recovered from metal ore through pyrometallurgical or hydrometallurgical processes. Pyrometallurgical processes use smelting to separate desired metals from undesired components and are the way a large percentage of metals produced today are obtained. A typical pyrometallurgical plant includes crushing, grinding, flotation, concentrating, smelting, and refining equipment. One disadvantage with pyrometallurgical processes is that certain metal ores cannot be satisfactorily treated by smelting. Another disadvantage of pyrometallurgical processes is that they create sulfur dioxide emissions. Still another disadvantage of pyrometallurgical processes is that they are less economically efficient.
Hydrometallurgical processes involve extracting metals from ores by dissolving them in aqueous chemical solutions. These processes are often more cost effective than pyrometallurgical processes. However, only certain ores, such as chalcocite (Cu2S), are leachable and thus amenable to hydrometallurgical treatment. Still further, controlling the leaching operation in the hydrometallurgical process is difficult in regions that have heavy or continuous rainfall because of the resulting high silt levels in the leachate.
Currently, conventional hydrometallurgical plants include multiple sets of dynamic pumper-mixers and large settlers that primarily use gravity to separate components in the various stages of hydrometallurgy including extraction, scrubbing, and stripping. Dynamic pumper-mixers, which have dynamic agitators, combine mixing and pumping functions in one piece of equipment. Thus, when increased flow rates are required, the dynamic mixer""s speed (rpm) must be increased. The shear imparted by a dynamic mixer/agitator increases with the angular velocity of the agitator, which in turns increases with the radius of the impeller blade and pumper shroud. When agitation speed is increased, the higher shear creates a wider distribution of particle sizes, including the generation of a fine entrainment.
Dynamic mixers and mixer boxes that are conventionally used in hydrometallurgical plants are typically sized so as to require at least about 2 minutes of mixing. Still further, conventional settlers used in hydrometallurgical plants require approximately 6 to 8 minutes for settling because they are normally large vats that work only by allowing gravity to separate an emulsion mixture into a lighter organic phase and a heavier aqueous phase.
One disadvantage with the dynamic pumper-mixers that are currently used in hydrometallurgical plants is that they provide poor process control. For example, they have poor entrainment control for both oil phase into aqueous and vice-versa. As a result, conventional plants have higher operating costs because entrained fluid must be replaced, and certain entrained contaminants require treatment steps, although these combined costs are generally less expensive than the operating costs of pyrometallurgical plants. A disadvantage of conventional settlers is that large and unstable gunk layers (an emulsion of solid particulates, organic, air and aqueous solutions) regularly build up in the settler due to the dynamic mixer action and air being entrained by the mixer. When operating it, oil/aqueous (O/A) ratios close to 1/1, the gunk layer is unstable, and phase inversions occur frequently which require extensive operator attention to remediate. Another disadvantage with conventional hydrometallurgical equipment is that it requires a large inventory of expensive organic solution to be used in the settler(s) to allow gravity separation to take place, and because entrained organic solvent is created by excess shear, it is lost back to the leach areas. Furthermore, such plants can often be inefficient in transferring metal to an organic solution. Still further, entrained aqueous contaminants require expensive bleed streams and special additives in conventional plants in order to maintain a high quality metal electrolyte solution for making metal cathodes in the electrowinning tankhouse. Lastly, ions of iron in the aqueous entrainment reduce electrolytic efficiency by wasting electrical energy on the Fe+++⇄Fe++ reaction.
In addition to the inefficient equipment in use in conventional hydrometallurgical extraction plants, another problem with these plants is that they are fixed in one location. Therefore, it becomes necessary to pump leach solutions back and forth from remote locations as a mine site matures and expands. Still another problem with such conventional plants is that they are basically open systems, which allows air entrainment and air-borne dust into the system and allows air pollution from the evaporation of the organic. Indeed, environmental regulations are forcing the installation of covers over the entire apparatus. A further problem with conventional hydrometallurgical extraction plants is that they require large amounts of flat surface land area for construction in a location that is normally hilly or mountainous. Thus, large capital expenditures are required to build such mineral processing plants.
Another disadvantage with hydrometallurgical plants is that during the leaching step of a hydrometallurgical process, contaminants, such as iron, manganese, and chlorides, are often leached along with a desired metal by a raffinate and enter into the hydrometallurgical plant as part of the pregnant leach solution. These contaminants are then transferred to the metal electrolyte solution via either entrainment or by the chemical binding of the contaminants to the organic solution used in the extracting stage. When these contaminants are found in the metal electrolyte solution, which is to be sent to the electrowinning tankhouse, this contamination, especially iron contamination, has a serious impact on the electrical deposition current efficiency of the metal electrolyte solution. Also, manganese will attack the anodes and thereby reduce their usable life.
A conventional contaminant and/or secondary metal removal strategy includes construction of an organic scrub circuit, which includes a dynamic pumper mixer-settler. The wash or scrub solution is one that is lean in the contaminant or secondary metal. The dynamic pumper mixer-settler acts to flood the organic solution that includes contaminants with a scrub solution, can simply reduce the concentration of contaminants in the system by dilution, or can chemically remove contaminants by extraction into the aqueous phase. This organic wash circuit works by continuously bleeding out contaminants. In such a process, large volumes of bleed streams result as waste. Fresh make-up solution is then required to keep the recirculating stream whole. One disadvantage with such a method is that the removal of contaminants by this method is typically 40% to 50%. Still another disadvantage with a conventional organic wash circuit is that it is capital intensive in its initial construction. It is also expensive to operate because large volumes of bleed streams and fresh make-up streams are needed.
In order to overcome the deficiencies found with conventional hydrometallurgical extraction plants, a solvent extraction plant that has an optimized extraction efficiency and capacity, a method for making such a plant, and a process for using such a plant are needed. In addition, such a plant should be a closed system. Still further, such a plant should be modular so that it can be moved easily to another location as a mine site matures and expands.
Still further, in order to remove contaminants that enter the hydrometallurgical plant from the loaded organic circuit before they enter the electrolyte plating circuit, an organic scrub station is needed that can effectively remove nearly 100% of the contaminants that have become bound to the pregnant leach solution and are then transferred to the loaded organic solution. Still further, this organic scrub station should be less; expensive in both capital and operating costs than conventional organic wash circuits.
It is an object of the present invention to provide a solvent extraction plant with physically smaller mixers and separation devices that require shorter residence times and therefore less organic solvent inventory so as to minimize capital costs.
Another object of the present invention is to provide a solvent extraction plant that applies an approximately uniform shear in the various mixing steps of the metal extraction process, even when the flowrates of various streams in the plant are increased, thus allowing a much narrower particle size distribution to result than when conventional dynamic pumper/agitators are used.
Still another object of the present invention is to provide a solvent extraction plant that is capable of providing improved quality metal from electrolyte solutions at a lower operating cost than conventional plants by reducing make-up additive streams and entrained solvent losses.
A further object of the present invention is to provide a compact, portable plant that can be readily relocated to alternate mine sites making it unnecessary to pump leach solutions back and forth from remote locations as a mine site matures, expands, or changes. The concentrated electrolyte solution may require pumping back to the tankhouse, but it is typically one-third the volume of the leach solution.
A further object of the present invention is to provide an extraction plant that is a closed system so that there will be no more than a minimal amount of air entrained during mixing, ambient dust entering the system, and evaporative losses of organic solvent.
Another object of the present invention is to provide a plant that can be less susceptible to phase inversions and crud/gunk layer expansions and overflows, so as to reduce the number of site operating personnel required for process control and operation.
Still another object of the present invention is to provide a hydrometallurgical plant that has a lower initial capital development cost and allows for lower operating costs than conventional hydrometallurgical plants.
A further object of the present invention is to provide an organic scrub station for treating loaded organic solution from the plant and a process for using this organic scrub station to remove nearly 100% of undesirable contaminants from the organic solution, so that fewer contaminants enter further hydrometallurgical processing stages, such as the electrowinning stage.
Another object of the present invention is to provide an organic scrub station for removing contaminants from the loaded organic solution created in the plant that requires less scrub solution than conventional equipment, thus allowing less money to be spent on scrub solution, and a process for using the same.
Still another object of the present invention is to provide a clean and simple process for removing contaminants from organic solution and equipment that is able to be used in this process, so that contaminants are removed rather than just being diluted away.
A further object of the present invention is to provide an organic scrub station for treating loaded organic solution from the plant and a method for using the same in order to remove contaminants that are chemically bound to an organic solution.
Still another object of the present invention is to provide a method for making and a method for using the plant described above.
According to the present invention, certain of the foregoing objects and other objects are achieved by a modular solvent extraction plant, a method of making the same, and a method of using the same. This modular solvent extraction plant is downstream of a leach site containing metal ore where acid-enriched raffinate is fed into the leach dump or heap, and the raffinate leaches metal from the metal ore, forming a pregnant leach solution (PLS). In high volume hydrometallurgic plants requiring few theoretical stages, the PLS is then pumped to a stage-wise, plug flow contactor(s) that mixes the pregnant leach solution with an independently pumped barren organic solution to form a mixed emulsion. During the mixing process, the metal is extracted by and transferred to the organic solution, resulting in a loaded organic solution and a metal depleted raffinate as the components of the mixed emulsion. The mixed emulsion is then fed to a separator having corrugated sheet or parallel plate coalescing material in its first section. The separator separates the raffinate from the loaded organic solution. The raffinate is then fed into a raffinate coalescer, which removes organic entrainment from the raffinate. The loaded organic solution is then fed into a loaded organic coalescer unit, which removes raffinate entrainment from the loaded organic solution. The loaded organic solution is then fed into a second stage-wise, plug flow contactor, which mixes the loaded organic solution with a lean electrolyte solution. The metal in the loaded organic solution is transferred to the electrolyte solution leaving a mixture of a barren organic solution and a rich metal electrolyte solution. The mixture is then fed into a second separator that separates the metal electrolyte solution from the barren organic solution. This second separator also includes corrugated sheet or parallel plate coalescing material in its first section. The metal electrolyte solution is then fed into an electrolyte coalescer unit, which removes organic entrainment from the metal electrolyte solution. The metal-rich electrolyte solution is then fed to an electrowinning tankhouse, wherein metal cathodes are formed.
Additional objects are achieved by an organic scrub station for treating loaded organic solution from the plant and a process for using the same. The organic scrub station includes a stage-wise, plug flow contactor that mixes a scrub solution and loaded organic solution from the plant, which is comprised of an organic solution, a desired metal and certain contaminants, into a mixed emulsion, a separator connected to the contactor and having a first section comprised of coalescing material for breaking up the emulsion and a quiet zone for further separation of the scrub solution and the loaded organic solution, and a coalescer for receiving the loaded organic solution from the separator, wherein the coalescer removes scrub solution entrainment from the loaded organic solution. Still another aspect of the present invention is a process for removing contaminants from the loaded organic solution created in the plant using the organic scrub station of the present invention. This process involves mixing a scrub solution and a loaded organic solution, which is comprised of an organic solution, a desired metal and contaminants, into an emulsion, wherein said contaminants are transferred to said scrub solution, separating the emulsion into a scrub solution containing contaminants and a loaded organic solution, and polishing the loaded organic solution by feeding it through a coalescer so as to remove scrub solution entrainment.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.